Ambitious “Super Sewer” Finally Complete After Decade Of Construction

After a decade in the making, London’s ambitious “super sewer” is finally complete. The £5 billion (US$6.3 billion) Thames Tideway Tunnel promises to revolutionize the city’s wastewater management by significantly expanding the capacity of its outdated Victorian-era sewer system.

London’s original sewer system, built over 150 years ago, was designed for a population of around four million. However, with the city now housing more than double that number, the aging infrastructure had been struggling to cope. As a result, untreated sewage and stormwater frequently overflowed into the Thames, polluting the river and harming local ecosystems.

The new super sewer integrates with London’s existing system at 21 different points, increasing its overall capacity and reducing pollution. Spanning 25 km (15.5 miles), its main tunnel has a diameter of 7.2 meters (23.7 ft)—large enough to fit three London double-decker buses side by side. Additional connection tunnels range from 5 meters (16.4 ft) to 2 meters (6.6 ft) in diameter. Altogether, the tunnel can hold up to 1.6 million cubic meters (56.5 million cubic feet) of sewage, preventing it from reaching the Thames.

Construction on the project officially began in 2016 at 24 sites across London. To excavate the tunnels, engineers deployed six massive tunneling machines, each named after inspirational women from the local area, including pioneering scientists, doctors, and social activists. More than 20 deep shafts—some as wide as the dome of St. Paul’s Cathedral—were dug to facilitate the tunneling process.

With the system now operational, it has already prevented the equivalent of 2,200 Olympic-sized swimming pools of sewage from contaminating the river. While this marks a major milestone, further testing will continue to ensure the tunnel performs effectively under storm conditions.

“This is another significant step forward – with this final connection complete, the super sewer is fully up and running and protecting the Thames,” said Tideway CEO Andy Mitchell.

“Our next step is to test it in storm conditions – which is why we are keeping a close eye on the weather – and we will do this over the coming months. We are at the start of a new chapter for London and its river.”

The completion of the Thames Tideway Tunnel signals a new era for London’s wastewater management. Beyond just an infrastructure upgrade, the project aims to create a cleaner, healthier river environment, benefiting both local wildlife and city residents.